[app-server][core] Add connector-level Guardian reviewer overrides

[zamoshchin-openai]

approvals_reviewer = "auto_review"

[apps.connector_5f3c8c41a1e54ad7a76272c89e2554fa]
enabled = true
approvals_reviewer = "user"
default_tools_approval_mode = "prompt"

---

approvals_reviewer = "user"

[apps.connector_5f3c8c41a1e54ad7a76272c89e2554fa]
enabled = true
approvals_reviewer = "auto_review"
default_tools_approval_mode = "prompt"

Summary

• add apps.<connector_id>.approvals_reviewer to override Guardian or user review routing per connected app
• apply overrides across direct app MCP calls, delegated MCP prompts, and app-server MCP elicitation review while preserving global behavior for non-app MCP servers
• expose and document the config through app-server v2 and generated schemas, while honoring global managed reviewer requirements